Engines may be configured to operate with a variable number of active or deactivated cylinders to increase fuel economy, while optionally maintaining the overall exhaust mixture air-fuel ratio about stoichiometry. Such engines are known as variable displacement engines (VDE). In some examples, a portion of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, as well as various other operating conditions including vehicle speed. A VDE control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves, or through the control of a plurality of selectively deactivatable fuel injectors that affect cylinder fueling. By reducing displacement under low torque request situations, the engine is operated at a higher manifold pressure, reducing engine friction due to pumping, and resulting in reduced fuel consumption.
There are a few examples of how deactivating engine cylinders is typically conducted in a four-stroke engine that includes intake, compression, combustion (power), and exhaust strokes. In a first example, during the intake stroke an air-fuel charge is drawn into the cylinder, the air-fuel charge is compressed, spark is provided resulting in combustion, but rather than exhausting the combustion gases, the exhaust valve is maintained closed. This traps the high-pressure charge in the cylinder. An advantage to this methodology is lower oil migration/consumption as the high pressure in the deactivated cylinder prevents migration of oil into the cylinder. However, such a method has a distinct disadvantage in that there is a noticeable torque bump at deactivation, and a pumping penalty is realized for the first event after deactivation (which is small if deactivating for short periods, but significant if deactivated and reactivated often).
Another example of cylinder deactivation includes the same steps as above in the first example, but rather than trapping the high-pressure charge, the cylinder is exhausted, but rather than re-inducting an intake charge after the exhaust stroke, a vacuum is trapped in the cylinder by closing the exhaust valve (while maintaining closed the intake valve). Such an example has an advantage over the first example, in that there is a reduction in noticeable torque bump at deactivation, and increased fuel efficiency when deactivated and activated often, due to lower pumping work. However, a distinct disadvantage to such methodology is that by trapping the vacuum in the cylinder, oil consumption may increase. Increased oil consumption may result in at least two undesirable issues. The first may include oil fouled spark plug(s). A second issue may include the fact that crankcase vapors and/or oil migrating from a crankcase to the cylinder may result in a combustible mixture, which may result in a combustion event in the cylinder. Disabling spark during cylinder deactivation may prevent unintended combustion of crankcase vapors/oil migration, however oil fouling and oil migration may still result in spark plug degradation (spark plug fouling).
U.S. Pat. No. 9,261,067 B2 teaches a method for reducing spark plug fouling in deactivated cylinder(s), comprising supplying spark at a particular determined instance while the cylinder(s) are deactivated. However, the inventors have recognized an issue with such an approach. For example, the supplying of spark is not specified with relation to engine cycle status, or position of a piston(s) coupled to the cylinder(s). As such, providing spark according to U.S. Pat. No. 9,261,067 B2 may result in undesired combustion events while the cylinder(s) is deactivated.
Thus, the inventors herein have developed systems and methods to at least partially address the above-mentioned issues. In one example, a method comprises reducing fouling of a spark plug in a cylinder of an engine configured to propel a vehicle by providing a spark to the cylinder after the cylinder has been deactivated, where the spark is provided when a piston coupled to the cylinder is within a threshold of bottom dead center. By providing spark when the piston is within the threshold of bottom dead center, undesired combustion events may be reduced or eliminated, while spark plug fouling may additionally be reduced or eliminated.
As one example, the engine may comprise a variable displacement engine, and where providing the spark to the cylinder after the cylinder has been deactivated occurs in response to the cylinder being deactivated via trapping a negative pressure with respect to atmospheric pressure in the cylinder at deactivation. In such an example, trapping the negative pressure at deactivation may include exhausting a combusted mixture of air and fuel to an exhaust system of the engine, and then sealing the cylinder from atmosphere.
In examples where a plurality of cylinders are selected for deactivation, such a method as that described above may include providing spark to the plurality of cylinders in response to deactivation of the plurality of cylinders, at the predefined position of a plurality of pistons coupled to the plurality of cylinders.
In some examples of such a method, a spark ignition energy comprising the spark provided to the cylinder after deactivation of the cylinder, is variable. For example, spark ignition energy may be increased after a predetermined number of spark events, while the cylinder is deactivated. Furthermore, in some examples, a spark frequency of the spark provided to the cylinder may be variable as a function of vehicle operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.